CA1143030A

CA1143030A - Pressure-sensitive transducer and apparatus

Info

Publication number: CA1143030A
Application number: CA000360825A
Authority: CA
Inventors: Franklin N. Eventoff
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-09-24
Filing date: 1980-09-23
Publication date: 1983-03-15
Also published as: US4315238A

Abstract

ABSTRACT

A pressure responsive, variable resistance, analog switch has first and second conductors interleaved in spaced-apart relationship and disposed on a base member. An insulative spacer ring is positioned around and rises above the first and second conductors. A resilient cover sheet is attached to the top of the insulative spacer ring in spaced relationship over the conductors to define an enclosure between the resilient cover sheet and the base member. A
pressure sensitive resistive conductor composition is disposed on the resilient cover sheet or on the conductors in the enclosure to interconnect a resistance between the first and second conductors when the resilient cover sheet is depressed against the conductors. The amount of resistance so interconnected varies inversely to the amount of pressure exerted.

Description

., ~ I
~1~3~0 E~ACKGROt~ND OF T~ Il'lVE~ N

3 The present invention relates to pressure 4 ,~ sensitive variable resistance devices and in particular 5 1~ relates to pressure sensitive variable resistance switches 6 ¦ particularly useful on a keyboard for an electronic musical 7 instrument which actuates the generation or changing of a 8¦ tone and thereafter causes analog variations in the volume 9~ or tonal characteristics in response to the application of a 10l greater or lesser depression of force on the switch.

12 ! The generation of musical sounds by electronic -13 means is well known. Mowever, one problem which exists in 14 most electronic instruments is the inability to continuously 15 ~ vary either the volume or the tonal quality of the sound 16 generated. This inability limits the musician's freedom of 1~ musical expression. The present invention provides a novel 18 yet simple pressure responsive analog switch having a

2~ 1 contact resistance which varies inversely to the amount of pressure applied to depress the analog switch. ~hen 21 used in electronic musical instruments, a plurality of such 22 analog switches may be placed side by side in an elongated 23~ fashion to provide a keyboard or one such switch may be used 241~ to effect changes in tone by altering the characteristics of one or more tone aenerating circuits in the musical instrurrent.
26 ! ' ' ' ~,-11 .~

3~3~ 1 1 ll Pressure sensitive analog switches have been 2 I known. For example, both in Ruben, Patent No. 2,375,178, and 3 ll Costanzo, Patent No. 3,386,067, analog switches are disclosed

4 ll which sandwich a fibrous or sponge~like Iayer containinq a

5 l¦ conductive material between two conductor plates. As the

6 ¦~ two conductor plates are compressed together the number of

7 1~ electrically conductive paths through the sandwiched layer

8 volume increases, thus decreasing the electrical resistance

9 through that layer. In each of these devices, however, the resistive sandwich layer must be resilient to force the 11 electrodes apart and disconnect most of the conductive paths 12 when the compression force is released. Furthermore, the 13 semiconducting sandwiched layer depends on macroscopic 14 compaction to increase the number of electrical conductive 15 I paths between the upper and lower conductor plates. Conse-16 ~ quently, the sandwiched layer must have a relatively large 17 I thickness. Finally, in such devices the resiliency of the 18 fibrous or sponge-like layer can decrease with-use, thus 19 causing a degeneration in the operating characteristics of the switch.

22 In Mitchell, Patent No. 3,806,471, a pressure 23 responsive semiconductor material such as molybdenum disulfide 241 was disclosed, placed between conductor plates to provide an 251 ad~ustable resistor or transducer. ~owever, Mitchell relies 26 on volume resistance, that is, the resistance through a ~ 3 3~
1 I relativelv thick volume of the molybdenum disulfide layer.
2 ¦I The present invention on the other hand uses the contact or 3 l~ surface resistance of a very thin layer of molvbdenum 4 l¦ disulfide. ~ore specifically, Mitchell discloses a molybdenum 5 !~ disulfide volume (thickness) of .001 to 1.0 inch using 6 ~ molybdenum disulfide particles in the range of 50 to 7 1 60n mesh to provide a high but finite number of three-8~1 dimensionally distributed current flow paths through the 9 ~ resistive ~aterial. Under compression, the number of

10~ current flow paths between the particles in the volume

11~ increases, thus causing the resistance to decrease. The 12l semiconductor volume layer is the~ permanently positioned 1 13 and attached between two conducting electrodes. I
14 In addition to the above-described functional 15 distinction, the structures disclosed by Mitchell re~uire 16 I that the semi-conducting volume be positioned between two 17 electrodes or conductors or otherwise be positioned between 18 a conductor and a nonconductive plate or member so that the 19 semiconducting composition layer does not have any exposed surfaces but rather is in intimate contact with either the 21 insulative plate or the conductors. Such a configuration is 22 fundamentally different from applicant's invention where the 23 semiconducting composition layer must necessarily have at 24 least one contact surface which is not in intimate contact with either a conductor or another semiconducting layer.
26~¦ Such an arrangement facilitates taking advantage of the ~ 4 \ :
3(~ 1 1 ~I physical contact resistance over the surface of the composi- ¦
2 I tion rather than ta~ing advantage of the surface resistance 3 ~ of the individual particles of material on which ',itchell 11-4 ¦ primarily relies.

6 ¦ The present invention also is exemplified by 7 1 the use of particle sizes on the order of one micron and ~ layer thickness, preferably less than .001 inch. Furthermore, 9 1 since the variable resistance occurs because of a greater or lesser number of surface contact locations, one surface of 11 the semiconductor layer must be at least initially spaced

12 apart from one of the conducting electrodes or must be in

13 nonintimate contact with the opposing surface, although it

14 may be in touching relationshp therewith. Depression of the

15~ conducting electrode against the surface of the thin semicon-

16 ¦ ductor layer results in a plurality of contact points

17 ¦ being made along the surface. These contact points increase

18 as pressure is applied, thus decreasing the resistance

19 between the conducting plates or contacts on either side of the semiconductor layer. Of course, the sur~ace contact 21 semiconductor layer must be made of any suitable semiconductor 22 material.

24 A signiEicant advantage of the thin semicon-ductor layer of the present invention is that the semiconductor 26 material u;ed to form the layer may be combined with a 3~3t~ 1 binder and a binder thinner and thereafter sprayed or 2 l~ sil~-screened onto the desired surface to form a layer 3 I having a thickness as little as one mil or less. Manufactur-4 ¦I Lng costs for both labor and materials are thus greatly decreased.

7 In addition to the above advantages, the use 8 of molybdenum disulfide to cover the conductive layers 9 effectively protects the surface of the conductor from contact with the air. This alleviates a serious problem 11 which has been attendant with using conductors which slowly 12 corrode when exposed to the air. For example, copper 13~ conductors corrode when exposed to the air. This has .
14 necessitated the use of expensive silver or other similar 15 ¦ and likewise expensive conductive materials. However, when 16 molybdenum disulfide is sprayed or otherwise disposed to 17 cover the conductor, corrosion is greatly reduced which m~kes possible 18 the use of much less expensive conductor materials such as copper.
21 Stlll another significant advantage of the embodi-22 ment of the~ invention where either a conductor and a semicon-23 ducting layer surface or two semiconducting layer surfaces 24 are positioned in nonintimate but touching relationship rather than being spaced apart, is that chatter which is 26 inherent i~ ost switches ~s gre~tly reduced if not ellmin~ted 1 il entirely, Even if the chatter does exist, however, it 2 ¦1 occurs only when the resistance across the contact of the 3 ¦ switch apparatus is so great that the variations in voltage 4 1I due to the variations in resistance, which cause ~he chatter 5 ¦~ will be very small. Consequently, the resultant switch 6 il structure in this embodiment is bounceless. Such bounceless 7 ¦ switches have significant and substantial commercial 8 applications in the computer industry where there is a 9 constant need for improved bounceless switches of the type disclosed herein. Furthermore, not only is the switch 11 bounceless but it is substantially less expensive than prior 12~ bounceless switches.

14 In Pearlman, et al., Patent ~o. 4,044,642, a touch sensitive resistance device is disclosed for use in 16 musical instruments. However, the device uses a semiconductor 17 material sandwiched between two conductor plates in a manner 18 similar to Ruben and Costanzo. Specifically, Pearlman, et 19 al. uses a resilient material such as foam rubber or foamed synthetic polymeric material which has a particulate material 21 such as graphite dispersed throughout. The switch structure 22 has a foam semiconductor layer and an insulator layer with 23 an orifice therethrough sandwiched between two conductor 24~ plates. Thus, when a compression force is applied, the 25~ graphite-saturated resilient foam layer deforms into the 26¦ orifice in the insulator material to initially make electrical ., I

1 contact to thereby switch the musical instrument on.
2 ~herea~ter, additional compression ~orce causes the resistance 3 l~ between the two conductor plates to decrease in the manner 4 ll previously described, thereby altering the volume or 5 ¦~ tonal quality produced.
7 l¦ Because Pearlman, et al. uses a porous foam 8¦ material there is no problem of air compression in the 9~ cavity when the switch is depressed since the air may easily 101 escape and return through the porous resistive material.
~ Furthermore, Pearlman, et al. depends on the physical 12 ¦ resiliency of the graphite-impregnated foam material, thus 13 requiring a semiconductor layer of substantially greater 14 thickness than with the present invention. In addition, a 15 ¦ degradation in mechanical resiliency of the semiconàuc-16~ tor layer also causes a degeneration in switch performance.

18~ It is therefore desirable to provide an analog 19¦ switch which has a pressure sensitive variable resistance in the ON state but which does not rely upon the resiliency of 21 the semiconductor layer to cause the switch to turn to an 22 OFF state when the compression force is removed. Furthermore, 23 it is desired to provide an analog switch without relying on Z4 the volume resistance through a relatively thick semiconductor layer permanently attached between two conductive plates or 26~ electrodes.

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i;31 130 --1 1I SUMMA~Y OF THF, I~`IVENTION
2 ~1 - 3 1l The present invention comprises a pressure responsive 4 1l analog switch having a resistance which varies inversely to the amount of compression force applied to the switch.
6 Specifically, the analog switch has a base member on which 7 ~ first and second spaced contact conductors are disposedO An 8 ¦ insulative spacer is positioned on the base member around 9 the contact conductors with a cover fixed to the insulative spacer, spaced above the contact conductors. The space 11 between the cover and the contact conductors defines an 12 enclosure surrounded on its sides by the spacer. ~he 13 cover is resiliently movable toward the contact conductors 14 in response to an external compression force. A pressure sensitive semiconductor ply is then positioned in the 16 enclosure between the cover and the contact conductors for 17 providing a variable resistance path between the first 18 contact conductor and the second contact conductor when the 19 cover is moved into physical contact with them. The resis-tance of the pressure sensitive semiconductor ply varies in 21 response to variations in the externally applied compression 22 force. Fin~lly, a passageway is provided between the 23 enclosure and the external region of the analog switch for 24 allowing free airflow into and out of the enclosure when tne 25l cover moves away from or towards the contact conductors.

Il l )30 `-- I

1 j, In one embodiment, the pressure sensitive 2 ~ semiconductor ply comprises a thin, pressure sensitive, 3 il semiconductor composition layer disposed on the surface of 4 11 the resiliently movable cover. ~n a second embodiment, the S ¦ pressure sensitive semiconductor ply comprises a third 6 conductor, such as a layer of silver, on the surface of the 7 cover in the enclosure and a pressure sensitive semiconductor 8 composition layer disposed on at least one of the first and 9 1 second contact conductors.

11 In still another embodiment of the invention, a 12 bounceless switch apparatus is provided having a surface 13 contact resistance which varies inversely with a pressure 14 applied normally thereto. The bounceless switch apparatus includes a first conductor member with a first pressure 16 sensitive composition layer disposed thereon. The first 17~ pressure sensitive composition layer includes a particulated 18 semiconducting material disposed for covering the first 19 conductor member in intimate electrically conducting contact therewith and further has a first exposed surface. A second 21 conductor member is then provided in touching but nonintimate 22 relationship to the first exposed surface of the first 23 pressure sensitive composition layer for providinq a 24 variab]e surface contact junction.
/ / /

, ~ 10 I, ~1~3030 In an alternative embodiment the second conductor member may have disposed thereon a second pressure sensitive composition layer likewise including the partic~lated semiconducting material disposed for covering the second cond~ctor member and for being an intimate electrically conducting contact therewith. The second pressure sensitive composition layer then has a second exposed surface ~here the first and second exposed s~rfaces of the first and second press~re sensitive composition layers respectively are positioned in touching b~t nonintimate relationship with each other for providing a variable s~rface contact ~nction.
According to another aspect of the invention there is provided a method of evenly distributing a dry semi-conducting layer on a surface so that the semiconducting layer is of a substantially constant thickness of less than .001 inch for making a pressure sensitive force transducer com-prising the steps of:
preparing a solution comprising a mixture of at least a semiconducting particulate, a binder, and a binder solvent wherein the amounts of binder and particulate are selected so that the weight ratio of binder to particulate in a resultant dry semiconducting layer is on the order of about one-to-one, and the amount of binder solvent is selected so that the solution of at least binder, particulate and binder solvent is of a sprayable consistency;
spraying the solution on the surface for forming a wet semiconducting layer of substantially constant thickness;
and allowing the sprayed solution to dry to form the dry semiconducting layer on the surface whereby conduction across the surface of thesemiconducting layer varies in response to variations in pressure applied to the semicon-ducting layer.
There is also provided a method of evenly dis-tributing a dry semiconducing layer on a surface so that the semiconducting layer is of a substantially constant thickness of less than .001 inch for making a pressure sensitive force transducer comprising the steps of:
preparing a solution comprising a mixture of at least a semiconducting particulate, a binder, and a binder solvent wherein the amounts of binder and particulate are selected so that the weight ratio of binder to particulate in a resultant dry semiconducting layer is on the order of about one-to-one, and the amount of binder solvent is selected so that the solution of at least binder, particulate and binder solvent is of a screenable consistency;
screening the solution on the surface for forming a wet semiconducting layer of substantially constant thickness;
and allowing the screened solution to dry to form the dry semiconducting layer on the surface whereby conduction across the surface on the semiconducting layer varies in response to variations in pressure applied to the semicon-ducting layer.
There is further provided in accordance with still -lla-11~3~30 another aspect of the invention a composition for forming a thin layer of less than .001 inch of a pressure-sensitive semi-conducting member having contact junction resistance across its surface which varies inversely with a pressure applied normally thereto, the composition comprising:
a quantity of particulate, a binder for the quantity of particulate, and a binder solvent for said binder and said particulate mixture, the ratio of the binder to solvent being such as to form said thin layer.

-llb~

1l h~ 30 `- , 1 _RIEF DESCRIPTION OF DRA~ G.

3 ~l A complete understanding of the present invention 4 ~ and of the above advantages may be gained from a consideration -~
5 ~ of the following description of the preferred embodiments 6 1 taken in conjunction with the accompanyins drawings in 8 which:
9 ¦ FIG[JRE l is a cross-sectional plan view of one embodiment of a pressure responsive analog switch with the 111 pressure responsive coating positioned between two conductor 12 plates in a spaced relationship.

14 FIGURE 2 is a cross-sectional plan view of a preferred embodiment of a pressure responsive analog switch 6 in accordance with the present invention.

18 FIGURE 3 is a cross--sectional plan view of an 19 alternative embodiment of a pressure responsive analog 2l switch with the thin resistive coating on the conductors.
22 F`~GURE 4 is a schematic representation of a 3 pressure responsive analog switch with the cover removed 24l showrl interconnected to a utili~ation circuit.
25 ~
26 ~

3~3~

1 ll FIGURE 5 is a cross-sectional side view of a 2 I bounceless switch apparatus.
3 ll 4 1 FIGURE 6 is a pressure versus voltaqe curve illustrating the variations in voltaqe across ~he semiconduct-6 ing composition layers as the compression forcinq those two 7 layers toqether is increased.
8 l 9 j FIGURE 7 is a curve illustrating the output of the 10 ¦ bounceless switch in accordance with the invention shown in 11 FIGURE 5.

13 FIGURE 8 is an illustrated embodiment of the .
14 bounceless switch apparatus in accordance with the invention lS having only one semiconducting composition layer.

20 /i/

21 / / /

24~ / /
25~ / / /

l~ 13 ~ .. I
~ 3~30 - I

1 ~ DETAILED ~ESCRIPTI0 2 ~
~ ¦Referring first to ~IG~RE 1, an analog switch in 4 ¦ accordance with the present inventionis shown comprising a 5 ~ first conductor plate 5Q spaced from a second conductor ¦ plate 52 by spacers 54 to define a gap or chamber 60 between 7 ¦ the first and second conductor plates 50 and 52. At least 8 ¦ one of the conductor plates 50 or 52 is resilient so that it 9 ¦ may be depressed against the other conductor plate to close 10 ~ the switch.
11 1~
12 ¦I The conductor plate may comprise a flexible 13 I support sheet 6~, such as Myla ~ with a thin conductive 14 ~ layer 66 of silver or other conductive material sprayed, 15 ¦ screened or otherwise applied on the surface of the support 16 ¦ sheet 64 adjacent the second conductor plate 52. The second 17 conductor plate 52 may comprise a rigid plastic base member 1~ 68 with a thin copper surface 70 disposed thereon. Of 19 course, it will be appreciated that the base member 68 may be flexible and the thin surface 70 may be made of 21 silver or other suitable conductive material. A lead 56 and

22 a lead 58 may be coupled to the silver layer 66 and the

23 copper surface 70 respectively to allow for electrical 245 coupling of the analog switch to a utilization circuit.

~D

3~30 1 ; Finally, a thin semiconductor layer 62 of semi-2 l' conductor material is sprayed, screened or otherwise evenly 3 ~ applied on the copper surface 70. Alternatively, the i semiconductor material 62 may be sprayed, screened or otherwise evenly applied on the conductive layer 66 or on 6 both the copper surface 70 and the conductive layer 66. The 7 ~ semiconductor material may be an-y suitable composition which 8 ¦ is sprayable, screenable, or otherwise of a consistency 9 I which may be evenly applied to form a smooth exposed 10 I surface. For example, the semiconductor material may be 11 molybdenum disulfide particulate having particle sizes on 12 the order of one to ten microns mixed with a binder material.
13 such as resin to form a liquid. A resin thinner may be 14 added to give the composition a consistency suitable for spraying. The thin semiconductor layer 62 of the semiconductor 16 material is then sprayed or screened on- the conductive layer 17 66 of the support sheet 64 or on the copper surface 70 on 18 the rigid base member 68. It will be apprecited, of course, 19 that the semiconductor layer may be of any thickness so long as there is an exposed smooth semiconductor surface.
21 However, in order to conserve on semiconductor material and 22 to minimize surface irregularities which may occur when 23 thick semiconductor layers are utilized, a thickness on the

24 order of about .001 inch or less is preferred.

25~ / / /

26 jl ///

1~ 15 I i I! i ~ i P30 ~' 1 1.
l ¦ The use of a very thin layer of sprayed or 2 !I screened semiconductor material allows the semiconductor 3 ~I material to be resiliently moved by the depression of the 4 1I conductor plate 50. Furthermore, since it is a surface 5 ¦I contact resistance effect and not a volume resistance that 6 causes a decrease in resistance when pressure is applied, 7 1 much less semiconductor material is required to be used and 8 ¦ fabrication of the switch is much faster, easier and less ¦

9 ll expensive than with prior art devices. The minimum resistance ; 10 through the semiconductor layer may be selected by control ; 11 of the ratio of semiconductor material to binder.
1~
13 Of course, it will be appreciated that the 14 semiconductor material may be brushed or screened or disposed on the selected surface in any suitable way so that a 16 uniform, smooth exposed semiconductor surface is provided.
17 It will also be appreciated that any semiconductor material 18 may be used so long as a large number of contact points are l9 provided on the semiconductor surface whereby variations in the pressure applied to press a second conductor against the 21 semiconductor surface will cause variations in the number of 22 contact points and hence, variations in the resistance 231 across the semiconductor material. The resistance through 24¦ the semiconductor layer can be varied by varying the 25~ semiconductor material to resin ratio. In the preferred 26 embodiment, because the phenomenon is based on surface l ~ l l~ 16 ~;303R

resistance, not volume resistance, the weight ratio of binder to semiconductor material is about one to one.
Referring to FIGURE 2, another embodiment of a pressure responsive, variable contact resistance analog switch 10 is illustrated having a base member 12 which may be rigid plastic, flexible Mylar (polyetnylene terephthalate) or any other suitable material. Contact conductors 13 cOmprising spaced first and second contact conductors 14 and 16 are disposed on one surface of the base member 12. An insulative spacer member 18 is affixed to the base member 12 around the contact conductors 13. A cover 19 is then positioned on top of the insultaive spacer 18 thereby defining an enclosure or chamber 24 between the cover 19 and the contact conductors 13.
In one embodiment, the cover 19 comprises a flexible support member 20 which may, for example, be a thin sheet of Mylar. The side of the flexible support member 20 facing the contact conductors 13 is Spr~yed with a pressure sensitive semiconductor composition layer 22 which may, for example, be a mixture of any suitable resin, e.g., acrylic resin, such as R-20 sold by Specialty Coatings & Chemicals, Inc., of ~orth Hollywood, California, and molybdenum disulfide.
In one embodiment the liquid composition to be sprayed is made by mixing 5 to 10 milliliters resin, 40 milliliters resin thinner, and 8.5 grams of molybdenum disulfide.

1 Of course, it will be appreciated that numero~s other resin 2 ~l and semiconductor material compositions may be used without 3 I departinq from the spirit of the present invention. Specifi--4 1ll cally, materials such as sponge iron powder and iron oxide, 5 ~ tungsten carbide powder, tin oxide powder, boron powder or 6 any other semiconductor material may be used, although 7 ~ molybdenum disulfide is preferred because of its low-noise 8 ~ lubricating characteristics.

9l 10l The resultant cover 19 is glued or otherwise 111 mechanically affixed to at least portions of the top of the 12¦ insulative spacer 18 so that the pressure sensitive resistive 13 layer 22 is in a normally spaced relationship (i.e., the .
14 switch is normally open) relative to the contact conductors 13. The glued or fixed cover is arranged to permit leakage 16 of air; otherwise, an air passageway must be provided as 17 referred to in other embodiments hereinafter.
1~
19 Referring to FIGURE 3, in an alternative embodiment of the invention, the pressure sensitive resistive layer 42 21 is disposed immediately on top of the contact conductors 13 22 and a conductor layer 36, such as a very thin layer of 23 silver, is disposed on the surface of the support member 24~ facing the resistive layer 42 on the contact conductors 25~ 13.
26~ / / /

1l '' ' .

3031~

1 ~l Of course other arrangements of the present il 2 ¦¦ invention are possible so long as a pressure sensitive 3 l~ semiconductor composition layer is positioned between the 4 I contact conductors 13 and the cover 19 so that when the cover 19 is depressed into a contacting relationship with & the contact conductors 13, the pressure sensitive resistive 7 composition layer 22, 42 or 62 (FIGURES 2, 3 or 1) will be 8 ¦ in series between a first contact conductor and a second 9 ¦ contact conductor. By exertinq more or less pressure to the resistive composition layer, more or less surface contact is 11 made causinq increased resistance between the adjacent 12 conductors.
13 1.
14 Referring again to FIGURE 2 as well as FIGURE 3, when the support member 20 is depressed, air trapped in the 16 enclosure 24 will be compressed and can be exhausted through, 1~ for example, the junction between the cover 19 and the 18 insulative spacer 18 or between the insulative spacer 18 and 19 the base member 12. When the pressure is then removed from the cover 19, the resilient forces of the support member 20 21 will be insuEficient to overcome the partial vacuum thus 22 created in the enclosure 24, causing the cover 19 to remain 23 in a depressed or closed state. This prevents the switch 10 24l from returning to a normally open state. In order to avoid 25~ this vacuum problem, a passageway in the form of an orifice 26¦ 26 extending through the base member 12 allows air to flow .~ ll 11 .

L3~113~) 1 1 1 into and out of the enclosure 24 when the cover is released 2 !~ or depressed. Of course it will be appreciated that any 3 11 other suitable pressure release mechanism may be incorpvrated 4 and for eYample the orifice 26 may be positioned through the 5 ~I cover 19 or through the insulative spacer 18. ~owever, in 6 ~ the preferred embodiment the passageway will be the orifice 7 ¦1 26 in the base member 12.

9 I Referring now to FIGU~E 4, a conductor pattern 10 I which may be used in accordance with the present invention 11~ is illustrated schematically. Specifically, a pressure 12 responsive variable contact resistance analog switch is 13 shown with the cover removed to illustrate the contact .
14 conductor patterns 14 and 16 and their interconnection to a 15~ utilization circuit 28. Specifically, a first lead 32 is 16 interconnected to one input of a utilization circuit 28 17 and terminates in a multiple diameter, opened ring, first 18 conductor pattern 16. A second lead 34 is coupled between a 19 second terminal of the utilization circuit 28 and a second contact conductor pattern 14 also comprised of a plurality 21 of opened circular conductors of varying diameters. The 22 circular portions of the first and second conductors 16 and 23 14 respectively are interleaved between one another in 241 spaced-apart relationship and are disposed on a base member 12 with the insulative spacer such as an insulative ring 18, 26 disposed around the periphery of the contact conductors 13.

I!

~ 3~3 ~;
1 1l Thus, by depressing the cover 19 an electrical path will be 2 I provided through a resistance 31 provided by the semi- ¦
3 ~I conductor composition layer between the first conductor 16 4 and the second conductor 14.

6 The range of resistance valves which may be 7 inserted between conductors 32 and 34 by applying pressure 8 may be increased by increasing the spacing between the .interleaved conductors 16 and 14.
10~
11 ¦ Referring now to FIG~RE 5, another embodiment of 12 ¦ the invention is illustrated for provlding a bounceless 13¦ switch apparatus having a surface contact resistance which 14¦ varies inversely with a pressure applied normally thereto.
151 Specifically, a bounceless switch apparatus 100 has a first 16¦ support member 102 which may be made out of ~Iylar, a rigid 171 plastic material, or any other suitable nonconductive base 18 material. A first conductor 104 is disposed on the surface 19 of the support member 102 with a first pressure sensitive composition layer 106 disposed thereon to cover and be in 21 intimate contact with the conductor member 104.

23 Ju~taposed normally opposite to the first pressure 24 sensitive composition layer 106 is an assembly comprising a s.upport member 110, which may be Mylar, rigid plastic, or 26 any other suitable nonconductive material, a conductor ., ~.1 ... .

~3030 member 112 disposed on one surface of the support member 110, and a second pressure sensitive composition layer 114 disposed to cover and be in intimate electrically conducting relationship with the conductor 112. The assembly comprising the second support 110, the second conductor member 112, and the second pressure sensitive composition layer 114 is positioned in facing relationship with the assembly compris-ing the first member 102 to the first conductor member 104 and the first pressure sensitive composition layer 106 so that the exposed surface 108 of the first pressure sensitive composition layer 106 is in nonintimate but touching relation-ship with the exposed surface 116 of the second pressure sensitive composition layer 114 to thereby define a nonintimate contact junction 1180 As previously indicated, the first and second pressure sensitive composition layers are made out of a particulated semiconducting material having particle sizes which are preferably on the order of one to ten microns, although larger sizes are possible. The particulated semiconducting material is then mixed with a binder material and, if necessary, a binder thinner, and then is sprayed, silk-screened or otherwise disposed on the conductors 104 and 112 respectively. Each resulting pressure-sensitive composition layer 106 and 114 thus has a number of particles which extend outwardly from the mean surface plane of the 3~)~30 1 I respective pressure sensitive composition layers 106 and 114 2 I to form micro protrusions of particulate semiconducting 3 1~ material. It is these microprotrusions which allow the 4 j first and second pressure sensitive composition layers to touch without beinq in intimate electrically conducting 6 relationship. ~owever, when pressure is applied compressing 7 ~ the two surfaces together, the microprotrusions on the 8 ¦ respective pressure sensitive composition layers are depressed 9 toward one another forming more and more electrical contact points, thus decreasing the resistance across the junction 11 118. However, because there is already a small number of 12 electrically contacting touching points (although these are 13 extremely few resulting in a very high resistance when 14 ~ the respective pressure sensitive composition layers are not being depressed against one another), the chatter which 16 results when mechanical contacts are brought into contact 17 with one another in conventional switches is virtually 18 eliminated. Furthermore, any chatter which might be 19 generated occurs only when the resistance across the junction 118 is extremely high thus making the voltage drop across 21 the junction 118 likewise very high thereby making the 22 voltage excursions or variation very small.

24 In operation the pressure is applied to compress 251 the respective pressure sensitive composition layers 26 towards one another so that the resistance across the ., I . '.
I

~ .
`" ~ 30 `~ ~

l;
1 junction 118 decreases as the number of contact points 2 ¦~ between the microprotrusions of the particulate semiconducting 3 1~ material increases thus causing the voltage drop across the 4 1l junction to decrease, This, in turn, results in an increase 5 ~l in the output voltage as illustrated by FIGURE 6 which 6 1l illustrates severally the increasing voltage on a lead 128 7 I coupling the conductor 104 to a threshold or utilization 8 I circuit 122. By coupling this voltage to the threshold 9 ¦ circuit 122, a clean bounceless and chatter-free transition 10 from the OFF to the ON state at the output of 130 of the 11 threshold circuit 122 can be achieved as generally illustrated '2 in FIGURE 7. -13 1.
14 Of course it will be appreciatc-d that a threshold circuit such as the threshold circuit 122 is a well-known 16 conventional circuit and indeed such a circuit is not 17 necessary in accordance with the invention in many types of 18 circuits, particularly those using CMOS-type circuitry 19 wherein inherent thresholding occurs in the circuit components used to perform other functions.
` 21 .
22 Referring now to FIGURE 8, an alternative embodiment 23 of the invention is shown in which only one of the conductors 2~ ¦ has a pressure sensitive composition layer disposed thereon.
25~ Specifically, a conductor member 132 is disposed on the top 26¦ of an insulative support member 130 with a pressure-sensitive : 2~

3~)3~

1 I composition layer 134 disposed to cover the conductor 132 2 ~l and be in initimate electrically conducting relationship 3 1l therewith. A sècond conductor member 138 is similarly 4 I disposed on a second support member 140. The second 5 ¦ conductor 138 is then positioned in nonintimate but touching 6 relationship with the exposed surface 136 of the pressure 7 sensitive composition layer 134. In a manner similar to 8 that previouslv described, the minute microprotrusions f ¦
9 semiconducting material allow the conductor 138 to be in touching but nonintimate and virtually nonconducting relation-11 ship with the semiconductin~ layer 132 thus resulting in an 12 extremely high jun~tion resistance between the conductor 138 13 and the pressure sensitive composition layer surface 136.

15- Although various particulate sizes and layer thic~-16 nesses are possible in accordance with the invention, it has 17 been found that there is an inverse relationship between the 18 amount of electrical chatter caused by closing or opening the 19 switch contacts and the size of the molybdenum disulfide particles. Thus, the finer the grain size of the molybdenum 21 disulfide, the smoother the transition from the OFF to the 22 ON state (or vice-versa) of the switch will be. Specifically, 23 it has been found that particle sizes less than one micron 24 and preferably about .7 microns provide a substantially chatter-free switch transition.
26 ~ 25-I ., 3~)3V `--`-1 ~ ~1hile this second embodiment works qenerall/ the 2 same as the prior embodiment, in the preferred embodiment 3 ll both conductors are covered with the semicond~cting particu-4 11 lated material to insure qreater sensitivity.

6~ ~7hile particular embodiments of the invention have 7 ~ been shown and descri~ed, it will be obvious to those 8 ¦ skilled in the art that changes and modifications may be 9 made ~ithout departing from the invention in its broader aspects, and therefore the aim in the appended claims is to 11 cover all such changes and modifications as followed in the 12 true spirit and scope of the invention. -/ / /

1~ / / /

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25 ~ / / /
261 /// - ~

~ -25(A)-I I

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Claims

1. A bounceless switch apparatus having a junction re-sistance which varies inversely with a pressure applied normally thereto, comprising:
a first conductor member;
a pressure sensitive composition layer including a parti-culated semiconducting material disposed for covering the first conductor member in intimate electrically conducting contact therewith, the layer pressure sensitive composition layer having a first surface with a multiplicity of microprotrusions of the particulate semiconducting material extending from the first surface for providing a multiplicity of surface contact locations; and a second conductor member positioned in substantially nonelectrically conducting relationship to the pressure sensi-tive composition layer whereby the bounceless switch apparatus is normally open, the switch being closed in response to a pressing force applied to urge the second conductor member and the first surface together for increasing the physical contact between the microprotrusions and the second conductor, to enable electrical conduction through the contacting micropro-trusions, the amount of electrical conduction increasing as the amount of pressing force is increased and decreasing as the amount of pressing force is decreased.

2. A bounceless switch apparatus having a surface con-tact resistance which varies inversely with a pressure applied normally thereto comprising:
a first conductor member;
a first pressure sensitive composition layer including a particulated semiconducting material disposed for covering the first conductor member in intimate electrically conducting contact therewith and further having a first surface having a multiplicity of microprotrusions extending therefrom;
a second conductor member; and a second pressure sensitive composition layer including the particulated semiconducting material disposed for covering the second conductor in intimate, electrically conducting contact therewith and further having a second surface having a multiplicity of microprotrusions extending therefrom, the first and second surfaces being positioned in normally electrically nonconducting relationship with each other, at least one of the first and second conductor members being resiliently movable in response to a pressing force applied thereagainst so that the multiplicity of microprotrusions extending from the first and second pressure sensitive composition layers are urged against one another to enable electrical conduction between the first and second conductor members, the amount of electrical conduction increasing as the pressing force is increased and decreasing as the amount of pressing force is decreased.

3. The bounceless switch of claim 1 wherein the first pressure sensitive composition layer is less than about 0.001 inch thick.

4. The bounceless switch apparatus of claim 2 wherein the first and second pressure sensitive composition layers are less than about 0.001 inch thick.

5. The bounceless switch of claim 1 wherein the particulated semiconducting material is particulated molybdenum disulfide.

6. The bounceless switch of claim 5 wherein the particle size of the particulated molybdenum disulfide is less than one micron.

7. A pressure responsive analog transducer comprising:
a first contact;
a second contact;
at least one semiconducting layer comprising at least a pressure sensitive semiconductor particulate material, the semiconducting layer disposed in normally spaced relationship with at least one of the first and second contacts, the semi-conducting layer having a surface positioned in normally non-electrically-conducting relationship with at least one of the first and second contacts, the surface having a multiplicity of microprotrusions extending therefrom, each providing a minute contact location, at least one of the first contact, second contact and semiconducting layer being resiliently responsive to an external pressing force for causing the multiplicity of microprotrusions extending from the surface of the semiconducting layer and at least one of the first and second contacts to variably press against one another to define a variably elec-trically resistive junction so that electricity conducts between the first and second contacts through the minute contact location of the microprotrusions on the surface so that the resistance across the variably electrically resistive junction decreases in response to an increase in the external pressing force and increases in response to a decrease in the external pressing force.

8. The analog transducer of claim 7, further comprising a cover wherein the semiconducting layer is disposed on the surface of the cover for providing a shunt between the first contact and the second contact when the pressing force is applied.

9. The analog transducer of claim 7 further comprising:
a cover and a third contact on the surface of the cover in facing relationship to the first and second contacts for selectively forming a shunt between the first and second contacts, the semiconducting layer being disposed to overlay at least one of the first, second and third contacts.

10. The analog transducer of claim 7, wherein the semiconducting layer further comprises a binder composition mixed with the semiconductor particulate material and the semi-conductor particulate material comprises particulated molybdenum disulfide.

11. The analog transducer of claim 4 wherein the molybdenum disulfide particles have a maximum diameter which is less than about 10 microns.

12. The analog transducer of claim 10 wherein the binder composition comprises an acrylic resin.

13. The analog transducer of claim 10 wherein the particulated molybdenum disulfide and binder mixture are applied so that the semiconducting layer has a substantially constant thickness and the exposed surface has a multiplicity of protruding particles each comprising a minute contact location.

14. The analog transducer of claim 10, wherein the weight ratio of binder to particulated molybdenum disulfide is about one-to-one.

15. The analog transducer of claim 11, wherein the weight ratio of binder to particulated molybdenum disulfide is about one-to-one.

16. A method of evenly distributing a dry semi-conducting layer on a surface so that the semiconducting layer is of a substantially constant thickness of less than .001 inch for making a pressure sensitive force transducer comprising the steps of:
preparing a solution comprising a mixture of at least a semiconducting particulate, a binder, and a binder solvent wherein the amounts of binder and particulate are selected so that the weight ratio of binder to particulate in a resultant dry semiconducting layer is on the order of about one-to-one, and the amount of binder solvent is selected so that the solution of at least binder, particulate and binder solvent is of a sprayable consistency;
spraying the solution on the surface for forming a wet semiconducting layer of substantially constant thickness; and allowing the sprayed solution to dry to form the dry semiconducting layer on the surface whereby conduction across the surface of the semiconducting layer varies in response to variations in pressure applied to the semiconducting layer.

17. A method of evenly distributing a dry semi-conducting layer on a surface so that the semiconducting layer is of a substantially constant thickness of less than .001 inch for making a pressure sensitive force transducer comprising the steps of:
preparing a solution comprising a mixture of at least a semiconducting particulate, a binder, and a binder solvent wherein the amounts of binder and particulate are selected so that the weight ratio of binder to particulate in a resultant dry semiconducting layer is on the order of about one-to-one, and the amount of binder solvent is selected so that the solution of at least binder, particulate and binder solvent is of a screenable consistency;
screening the solution on the surface for forming a wet semiconducting layer of substantially constant thickness;
and allowing the screened solution to dry to form the dry semiconducting layer on the surface whereby conduction across the surface on the semiconducting layer varies in response to variations in pressure applied to the semi-conducting layer.

18. The method of claim 16 or 17 wherein the individual particles of the particulate are less than about 10 microns in diameter.

19. The method of claim 16 or 17 wherein the binder is electrically nonconductive.

20. The method of claim 16 or 17 wherein the semi-conducting particulate is particulated molybdenum disulfide.

21. A composition for forming a thin layer of less than .001 inch of a pressure-sensitive semiconducting member having contact junction resistance across its surface which varies inversely with a pressure applied normally thereto, the composition comprising:

a quantity of particulate, a binder for the quantity of particulate, and a binder solvent for said binder and said particulate mixture, the ratio of the binder to solvent being such as to form said thin layer.

22. The composition of claim 21 in which the particulate has particle sizes in the range of about one to ten microns.

23. The composition of claims 21 and 22 in which the weight ratio of binder to particulate is about one-to-one.

24. The composition of claims 21 and 22 in which the binder is electronically nonconductive.

25. The composition of claims 21 and 22 in which the binder is acrylic resin.

26. The composition of claim 21 or 22 wherein the particulate is particulated molybdenum disulfide.

27. The composition of claim 21 or 22 wherein the particulate is a semiconducting particulate.